Key form bits, 'fff' and 'FFF'

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The key form bits of a DES control vector define the length of the key, either single (‘fff’), double (‘FFF’) or triple (also ‘FFF’). Bits 40 – 42 in the base (first 64 bits) of a control vector are for a key length of single, double, or triple, while bits 104 – 106 in the extension (second 64 bits) of a control vector are for a key length of double or triple. Note that the bits in the extension of a single-length control vector should all be zeros.

The key form bits of a DES control vector (‘fff’ and ‘FFF’) are shown in the figures provided in DES control-vector base bit maps.

Table 1 defines the meaning of the key form bits, along with the rule array keywords associated with these values when using the Control Vector Generate, Key Token Build, and Key Token Parse services.

Table 1. Key form bits, 'fff' and 'FFF'
Key form bits, 'fff' and 'FFF'
CV bits 40 – 42 (key form bits)	CSNBKTB, CSNBKTP, CSNBCVG keyword	Meaning
B'000'	SINGLE, KEYLN8	Single-length key (only ‘fff’, not ‘FFF’)
	DOUBLE, KEYLN16, MIXED (DATA key only)	Double-length DATA key. Left and right key halves not guaranteed unique, ignoring parity bits. Requires a Version X’01’ fixed-length DES key-token format which contains a CV valued to binary zeros, with key length flag (token marks) at offset 59 = X’10’.
	ZEROCV24 (DATA key only). Note: ZEROCV24 is equivalent to IBM Z KEYLN24.	Triple-length DATA key. Left, middle, and right key parts not guaranteed unique, ignoring parity bits. Requires a Version X’01’ fixed-length DES key-token format which contains a CV valued to binary zeros, with key length flag (token marks) at offset 59 = B’xx20 xxxx’.
B'001'	DOUBLE, KEYLN16, MIXED	Double-length key, right half of CV. Left and right key halves not guaranteed unique, ignoring parity bits.
B'010'	DOUBLE, KEYLN16, MIXED	Double-length key, left half of CV. Left and right key halves not guaranteed unique, ignoring parity bits.
B'011'	TRIPLE (Release 5.4 or later)	Triple-length key, left and right halves of CV must be equal. Left, middle, and right key parts not guaranteed unique, ignoring parity bits.
B'100'	N/A	Undefined. This is a control vector violation.
B'101'	DOUBLE-O	Double-length key, right half of CV. Left and right key halves guaranteed unique, ignoring parity bits.
B'110'	DOUBLE-O	Double-length key, left half of CV. Left and right key halves guaranteed unique, ignoring parity bits.
B'111'	TRIPLE-O (Release 5.4 or later)	Triple-length key, left and right halves of CV must be equal. Left, middle, and right key parts guaranteed unique, ignoring parity bits.